In a typical wireless communication network, communication terminals, also known as wireless devices and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a radio access node such as a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole wireless communication network is also broadcasted in the cell. One radio access node may have one or more cells. The radio access nodes communicate over the air interface operating on radio frequencies with the communication terminals within range of the radio access nodes with downlink transmissions towards the communication terminals and uplink transmission from the communication terminals.
A Universal Mobile Telecommunications System (UMTS) is a third generation wireless communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (′A/CDMA) and/or High Speed Packet Access (HSPA) for wireless devices. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN as e.g. in UMTS, several radio access nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS) have been completed within the 3GPP and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio access nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio access nodes, e.g. eNodeBs in LTE, and the core network. As such, the Radio Access Network (RAN) of an EPS has an essentially “flat” architecture comprising radio access nodes without reporting to RNCs.
When catering for communication terminals in extended coverage, one common measure to take is to blindly, i.e. not wait for acknowledgement from a receiving device, repeat the information transmitted. If the procedure on how the repetitions have been performed is known to the receiving device, it can make use of that knowledge to maximize processing gain, and improve probability of decoding the transmitted information.
With repeated transmissions, more radio resources are consumed and hence it is of interest to maximize the information transfer as much as possible to the receiving end.
One efficient way of receiver processing is to coherently accumulate the blindly repeated information, and by this maximizing the processing gain, provided some conditions are fulfilled. One of these conditions is that the radio channel is close to stationary during the repetition interval. If this is not the case, the coherency is fully, or partially lost.
Another way of receiver processing is to combine “soft bits” of different blindly repeated transmissions. The receiving process typically involves demodulating the data, and from the demodulating process a set of “soft bits” is received. A soft bit could be seen as an estimation from the demodulator on how certain it is that the received bit is a 0 or a 1. The higher soft bit value, the higher the certainty. Combination of soft bits does not require that the channel is stationary, or that the repeated transmissions are identical, e.g. a reordering of the transmitted bits is allowed. On the other hand, a higher signal-to-noise ratio is required for soft combining to be effective.
One possible way of receiver processing is therefore to apply coherent combining over subsets of consecutive repeated blocks, and further to apply soft combining between these subsets.
If coherency over repetitions is not achievable due to some reason, for example the radio propagation channel not being stationary, as pointed out above, just retransmitting the same information blindly is not the most efficient way of transmitting information.
Explicit signaling of information in a repeated transmission scheme is costly as the same information is sent multiple times resulting in a reduced performance of the wireless communication network.